1. Field of the Invention
The present invention relates to a fastening machine that drives a fastener or the like into a material.
2. Description of the Related Art
A fastening machine which drives a fastener, such as nails, into a material by using compressed air or the like as power (referred hereinafter to as a nail gun) is known. This kind of nail gun is provided with a nose on a housing that faces a material into which a fastener is driven. The nose is formed with an ejecting mouth and a push lever, which locks firing of the fastener when not in use, and by being pushed by a material into which a fastener is to be driven when used, releases the lock of firing of the fastener. A driver blade for firing the fastener is slidably arranged on the ejecting mouth of the nose. In this nail gun, a driver blade is driven by compressed air while the push lever being pushed onto the material into which the fastener is to be driven, to fire the fastener in the direction of the tip of the ejecting mouth to be driven into the material.
Incidentally, a material, of which a surface is coated with a gravel-containing tar, has been known as a material for a residential house for increasing its strength and maintaining waterproof properties. Typical examples of those include a sheet-like asphalt shingle used in a roof, a sheathing board used in a wall and the like. These are fastened to a base sheet with the fastener.
Regarding the nail gun described above, a nail gun equipped with an adjusting guide on a magazine unit has been disclosed, for example, in Japanese Unexamined Japanese Patent Application KOKAI Publication No. 2000-108052. The attaching work of fastening an asphalt shingle (a material into which a fastener is to be driven) to a base sheet using this nail gun will be briefly described below. An operator makes the front surface of the adjusting guide abut against the side end of a first asphalt shingle, into which a nail has been driven to fasten it to the base sheet to thereby secure the position of the housing. The end of a second asphalt shingle, into which a nail is driven to fasten to the base sheet is next abutted against the segment, where a nail is fired from a nail gun, thus matching the position of the second asphalt shingle. A nail is subsequently driven into the second asphalt shingle to fasten to the base sheet. At present, alignment according to the above method is in general widely used in the work to attach an asphalt shingle.
FIG. 8 also shows enlargement of the lower end of a push lever 13A in a conventional nail gun. This nail gun is provided with a tip member 131 at the tip of the lower end of push lever 13A. A super-hard material member 20 such as tungsten carbide and the like is provided on the surface of the tip member 131 facing a material 21 into which a fastener is to be driven. Furthermore, a chamfered section 24 is provided at the corner of the tip member 131. As described above, the second asphalt shingle 22 is aligned by making the end of second asphalt shingle 22 abut against the tip member 131 at the lower end of push lever 13A.
When this work is repeated for an extended period, the tip member in the push lever is worn to possibly shorten the tip member. When the tip member is worn, an operator cannot align the tip member and it further becomes difficult to readily align the material into which the fastener is to be driven using the nail gun, leading to undesirable results.
However, a chamfered section 24 of the conventional nail gun shown in FIG. 8 is more protruded than other sections, having more chance to contact with the gravel in an asphalt shingle, a wall and the like to wear out faster than other section after used for a longer period. When the chamfered section 24 is worn out, a radius of curvature of the chamfered section 24 becomes larger than thickness of the second asphalt shingle 22. As a result, the worn out chamfered section 24 runs on to the end of asphalt shingle 22. Consequently, alignment of the second asphalt shingle 22 becomes difficult and drastically reduces the working efficiency. An operator therefore replaces the lower end of push lever 13A whenever the chamfered section 24 of the tip member 131 is worn out, resulting in diminishing economic efficiency.
When wear in the lower end of push lever 13A progresses, the nail gun pushes the first asphalt shingle 21 at two locations, where a pair of the super-hard material members 20 protruded from the tip member 131 abuts against the first asphalt shingle 21, thereby failing to hold down and possibly form an unattached segment. In such a case, the lower end of push lever 13A also has to be replaced.
A super-hard material member is also generally expensive so that use of the super-hard material member has stayed at minimum. Therefore, structure of a conventional nail gun cannot effectively prevent the tip member 131 from wear.